Hydrocarbon resources such as bituminous sands (also commonly referred to as oil sands) present significant technical and economic recovery challenges due to the hydrocarbons in the bituminous sands having high viscosities at initial reservoir temperature. Steam-assisted gravity drainage (SAGD) is an example of an in situ (or in-situ) steam injection-based hydrocarbon recovery process used to extract heavy oil or bitumen from a reservoir of bituminous sands by reducing viscosity of the hydrocarbons via steam injection. Other steam-assisted in-situ processes include cyclic steam stimulation (CSS), steam flooding, a solvent aided process (SAP) where steam is also used, and the like.
A SAGD system typically includes at least one pair of steam injection and hydrocarbons production wells (a “well pair”) located in a reservoir of bituminous sands. The injection (upper) well has a generally horizontal section used for injecting a fluid such as steam into the reservoir for softening the bitumen in a region of the reservoir and reducing the viscosity of the bitumen. Heat is transferred from the injected steam to the reservoir formation, which softens the bitumen. The softened bitumen and condensed steam can flow and drain downward due to gravity, thus leaving behind a porous region, which is permeable to gas and steam and is referred to as the steam chamber. Subsequently injected steam rises from the injection well, permeates the steam chamber, and condenses at the edge of the steam chamber. In the process, more heat is transferred to the bituminous sands and the steam chamber grows over time. The mobilized hydrocarbons and condensate that drain downward under gravity are collected by a generally horizontal section of the production well, which is typically disposed below the injection well and from which the hydrocarbons (oil) are (is) produced. Several well pairs may be arranged at a well pad or within the reservoir to form a well pattern. Additional injection or production wells, such as a well drilled using Wedge Well™ technology, may also be provided.
Some chemical additives have been used with steam to enhance in-situ hydrocarbon recovery from bituminous sands. For example, surfactants, which are compounds that lower the surface tension of a liquid, the interfacial tension (IFT) between two liquids, or the IFT between a liquid and a solid, have been suggested for in-situ hydrocarbon recovery processes such as, for example, SAGD. In such processes, surfactants may act, for example, as detergents, wetting agents, emulsifiers, foaming agents, or dispersants, to facilitate the drainage of the softened bitumen to the production well.
Organic solvents, such as an alkane or alkene, have also been suggested for hydrocarbon recovery from bituminous sands, since condensed organic solvents can be utilized to dilute the softened bitumen so as to increase the mobility of the diluted bitumen to the production well for recovery.
Challenges remain in connection with applications of chemical additives such as surfactants and solvents under in-situ conditions due to, for example, the elevated temperatures and pressures under which such processes are effected, compatibility issues with salt and thermal stability of the chemical additives.